Remove the do-external-lib and do-gnu-lib targets, along with
external/lib/Makefile and crypto/external/lib/Makefile, replacing
them all with SUBDIRs directly from lib/Makefile.
compat/compatsubdirs.mk becomes simpler now, as everything is built
from lib/Makefile, meaning all the libraries will now be built under
compat so update the set lists to account for that.